There has been an increase in interest in processes for the manufacture of small devices in the field of biological and biochemical analysis. The manufacture of devices used for analytical testing uses techniques similar to those used in the electronics industry. Examples of these manufacturing techniques include photolithography and wet chemical etching. The devices are often made from solid substrates such as silicon and glass.
Microanalytical devices have been used for performing various analytical reactions. For example, U.S. Pat. No. 5,498,392 to Wilding et al. discloses a mesoscale device having microfabricated fluid channels and chambers in a solid substrate for the performance of nucleic acid amplification reactions. U.S. Pat. No. 5,304,487 to Wilding et al. discloses a mesoscale device having a cell handling region for detecting an analyte in a sample. The microchannels and chambers have a cross-sectional dimension ranging from 0.1 micron to 500 microns. U.S. Pat. No. 5,885,470 to Parce et al. discloses a microfluidic transport device made from a polymeric substrate having fluid channels that can be a few microns wide.
There has also been an increased interest in microneedle injection for the transdermal delivery of various drugs. The microneedle devices can have a plurality of microneedles with a length of a few hundred microns. One example of a microneedle device for delivering a drug to a patient is disclosed in U.S. Pat. No. 5,879,326 to Godshall et al. Microneedle drug delivery devices are able to penetrate the stratum corneum of the skin with less irritation. The stratum corneum is a complex structure of compacted keratinized cell remnants having a thickness of about 10-30 microns and forms a waterproof membrane to protect the body from invasion by various substances and the outward migration of various compounds. The delivery of drugs through the skin is enhanced by either increasing the permeability of the skin or increasing the force or energy used to direct the drugs through the skin.
One method of delivering drugs through the skin is by forming micropores or cuts through the stratum corneum. By penetrating the stratum corneum and delivering the drug to the skin in or below the stratum corneum, many drugs can be effectively administered. The devices for penetrating the stratum corneum generally include a plurality of micron size needles or blades having a length to penetrate the stratum corneum without passing completely through the epidermis. Examples of these devices are disclosed in U.S. Pat. No. 5,879,326 to Godshall et al.; U.S. Pat. No. 5,250,023 to Lee et al.; and WO 97/48440.
These devices are usually made from silicon or other metals using etching methods. For example, U.S. Pat. No. 6,312,612 to Sherman describes a method of forming a microneedle array using MEMS technology and standard microfabrication techniques. Although effective, the resulting microneedle devices are expensive to manufacture and are difficult to produce in large numbers. Thus, there have been recent efforts to form micro-devices from polymers.
The '612 patent to Sherman also describes a method of forming micro-devices from a polymer. A mold base having a number of micropillars extending therefrom is formed by microelectrode-discharge machining or by photolithographic processing. A thin layer of polymer is arranged on top of the micropillars. The layer of polymer is heated so it deforms around the micropillars, forming micro-devices. The microelectrode-discharge machining or photolithographic processing used to form the mold are time consuming and expensive processes.
U.S. Pat. No. 6,331,266 to Powell et al. describes a process to form a molded micro-device from polymers. In particular Powell et al. describe a method for forming a micro-device from plastic by injection molding, compression molding, or embossing. The method of Powell et al. focuses on forming the micro-device from a mold, and not the creation of the mold itself.
U.S. Pat. No. 5,250,023 to Lee et al. describes a polymer micromold and fabrication process for the mold. A mold assembly with micro-sized features is formed. The mold assembly has a hollow portion that is fabricated from a sacrificial mandrel. The mandrel is surface-treated and coated to form an outer shell. The mandrel is then etched away leaving the outer shell as the mold. The process described in Lee et al. can only produce a singular hollow mold at a time. The mold created is used in conjunction with polymer extrusion in which polymer is passed through the hollow mold.
The prior methods and apparatus for the manufacture of micro-devices for medical use have exhibited some success but are generally time consuming and expensive. For example, the process of Lee et al. can only form a mold for a singular device. Accordingly, a continuing need exists in the industry for an improved method for the manufacture of micro-devices.